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Discussion Starter #1
Hi all.
My carb was fixed for a gas leak. Since then, there is an irregular "pop" sound from the second I start the engine. You can hear it more when driving slow, when idle or when decelerating. It is pretty continuous but it is irregular (meaning the interval between the pops can be less than a second and up to 3 seconds).
What might be causing it?

Thanks
 

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Any other symptoms? Sluggish throttle response, incorrect idle, anything? Does the pop seem to always come from one side or both?

It could be an improper air/fuel mix adjustment, but it also could be a float sticking on one side.

A few more details can go a long way...
 

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Thanks for the quick response.
It runs completely normal most of the time if the engine is warm.
The only time I feel a real difference is when it is very cold and I didn't allow it enough time to worm up. It will then have troubles when I just start moving from a full stop by chocking and then pops and jumps forward.
The idle seems correct and I think the pop is more to the right side than the left but I can't say for sure (the side that was fixed in the carb was the left).
I can try and video record it later if it helps.
 

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Yes, a video might help.

Also, check all of your vacuum lines to make sure they are installed correctly. An open vacuum port or leaky line can make all sorts of strange symptoms appear. Since the carbs have been off, double check the boots where the carbs mount to the engine and airbox as well.

I'm pretty surprised that whoever repaired your carbs didn't repair both at the same time. That's usually pretty standard procedure. Did you have this done at a shop or someone you know or??
 

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Discussion Starter #5
Thanks for the quick response.
It runs completely normal most of the time if the engine is warm.
The only time I feel a real difference is when it is very cold and I didn't allow it enough time to worm up. It will then have troubles when I just start moving from a full stop by chocking and then pops and jumps forward.
The idle seems correct and I think the pop is more to the right side than the left but I can't say for sure (the side that was fixed in the carb was the left).
I can try and video record it later if it helps.
I tried recording it but the normal sound makes it impossible to hear the abnormal one. But I did find out that you can really feel air bursts from the left exhaust (the side that the carb was fixed).
I will have to see if it sits correctly in its place.

It wasn't fixed by a pro but by a friend. Sadly, I can't afford a mechanic right now.
 

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Understandable about the mechanic costs NuFlood. If I wasn't one myself, I'd never be able to afford a tenth of what I do. As crazy as it sounds, gotta love growing up, well, broke. Keep us posted on what you find and we will keep on with help tips and advice...
 

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Could that be a synchronicity issue? If one carb was rebuilt and not the other, the vacuum characteristics could have conceivably changed and caused it to have that low end or idle irregularity.
 

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Could that be a synchronicity issue? If one carb was rebuilt and not the other, the vacuum characteristics could have conceivably changed and caused it to have that low end or idle irregularity.
That is a possibility. Both carbs had to be removed for servicing the one side, which is why I'm very surprised only one was serviced. My current line of thought is checking the most common issues first... vacuum/air leakage at one of the attachment points, either boots or hoses. After that we move on to sync, air/fuel ratio, etc.
 

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Discussion Starter #9
So here is an update.
So both sides of the carburetor were "serviced" (the rings were replaced and they were cleaned, but space wasn't checked so they might actually not be opening the same size).
Today, I tried to check for vacuum leak by spraying carb cleaner and seeing if it will be sucked in from anywhere. I couldn't see anything conclusive but I went ahead and tighten everything again. I even bought a heat gun to soften the boots and the connections to the airbox and made sure everything fits.
I'm not 100% sure that there isn't a vacuum leak. The reason was that when I sprayed the carb cleaner, most of it dripped down but maybe maybe just a bit was sucked in (or evaporated) on both sides at the same amount. But the sound is only coming from one side.
I also have a small coolant leak only when I'm riding (small enough that there is still more than the minimum level but large enough that it stains the engine) from the metal parts that connect between the area of the radiator and the thermostat. I think that there is an O ring there. I'm comfortable replacing it but if I do, is it just putting it all back together or do I also need something to remove the air that will enter the system after taking things apart? (I can copy paste this part to another post so it will be easier to search later).

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For the coolant issue, there's a drain plug on the bottom of the water pump housing; drain from there and when you go to refill it it, just pour it in slowly through the radiator cap neck. When it gets to or near the top, give the hoses a few squeezes, that should help to burp out any trapped air. If you positively can't get all the air out - you will know because it will run hot - then you can take the radiator cap off while it's cool and start it up; then blip the throttle a few times, that should force any and all air out.
I just did the above, minus having to start it and make the engine do the burping and it's working great now. I had leaky o-rings on the pipes that go into the valve cover.

To the carburetor issue, it doesn't sound like a vacuum leak; usually they are noticeable. When you spray something on the boots and it sucks it in the engine RPMs will noticeably change. What are the turns on your carb idle screws? Stock standard I think is 2 and 1/8 or 1/4 turn out, and then you can dial it in from there. It's possible you have a worn needle somewhere.
 

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So here is an update.
So both sides of the carburetor were "serviced" (the rings were replaced and they were cleaned, but space wasn't checked so they might actually not be opening the same size).
Today, I tried to check for vacuum leak by spraying carb cleaner and seeing if it will be sucked in from anywhere. I couldn't see anything conclusive but I went ahead and tighten everything again. I even bought a heat gun to soften the boots and the connections to the airbox and made sure everything fits.
I'm not 100% sure that there isn't a vacuum leak. The reason was that when I sprayed the carb cleaner, most of it dripped down but maybe maybe just a bit was sucked in (or evaporated) on both sides at the same amount. But the sound is only coming from one side.
I also have a small coolant leak only when I'm riding (small enough that there is still more than the minimum level but large enough that it stains the engine) from the metal parts that connect between the area of the radiator and the thermostat. I think that there is an O ring there. I'm comfortable replacing it but if I do, is it just putting it all back together or do I also need something to remove the air that will enter the system after taking things apart? (I can copy paste this part to another post so it will be easier to search later).

Thanks
First, you generally won't be able to actually see the fluid being drawn into the system, unless it's a very major leak in which case you would have probably seen in previously. What you are looking for mostly isn't with your eyes, but your ears. Any new material entering into the air mixture will generally cause a change in engine RPM, either higher or lower. Listen for the changes in engine sound.

Next, spray carb cleaner is not a good choice for diagnosing a vacuum leak in this manner. The actual carb cleaner itself generally isn't flammable, so it's much, much harder to gauge a change in engine RPM. The engine will generally slow down instead of speeding up, which is much harder to notice if it's only a small amount, which is typically the case with a small vacuum leak.

I use a non-chlorinated brake cleaner for searching a vacuum leak like this. The liquid is flammable, plus it dries very quickly, enabling you to move from place to place without worrying if it's only a residual effect from a previous test spot. The brake cleaner will actually cause the engine to surge (higher RPM) which is much easier to detect. You want to look for the warning that says "extremely flammable" or similar on the can. There is also a non-flammable (chlorinated) variety of spray brake cleaner, and that version does not work for this use, so make sure you check the can closely.

A side note there is that I use this same brake cleaner in place of ether (conventional starting fluid). It works the same in that application, but is less volatile meaning less chance of overloading the engine causing damage to internal components (I have seen that happen, or more specifically, the results of that when they come into the shop to be repaired).

Now, reading back to the original post, let me ask a couple other questions...

Does this popping only occur when the bike is cold? I ask because we just had a decent cold snap here in FL (lower 30s), and mine stumbled a bit on one cylinder until it warmed up, then it evened out. If it only happens when the bike is cold, or has been sitting for a while (even a couple hours), there might be another cause of this.

Is it more noticeable on acceleration or decel? only at idle? steady RPM under load (riding at a constant speed)?
 
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